A gear-train is a mechanical system formed by mounting a plurality of gears on a frame so that the teeth of the gears engage. Gear teeth are generally designed to ensure that the pitch circles of engaging gears roll on each other without slipping, thereby providing a smooth transmission of motion from one gear to the next. The ratio of the pitch circles of mating gears defines the speed ratio and the mechanical advantage of the gear set. The simplest example of a gear-train has two gears. The input gear, also known as the drive gear, transmits power to the output gear, also known as the driven gear. The drive gear will typically be connected to a power source, such as a motor or an engine. In such an example, the torque or force output of the driven gear depends on the ratio of the dimensions of the two gears.
Gear rattle is an acoustic disturbance generated by a gear-train as a result of dynamic behavior of constituent gears. Generally, gear rattle is a result of an excitation force, such as angular speed fluctuations imparted to the input gear or an external input force applied to the frame that mounts the gear-train, and profile errors of the gear teeth. Tooth profile errors are typically an unavoidable consequence of the underlying gear manufacturing process. The tooth profile errors frequently result in increased gear lash, which can lead to repeated impacts and rebounds of meshed gear teeth. Typically, gear rattle is generated by such repeated impacts and rebounds of the meshed gear teeth, and is especially common in unloaded or lightly loaded gears. Gear rattle can be affected and dissipated or produced by the bearings that support the gears and respective gear lubrication conditions.